Materials Data on BaCa(FeO2)4 by Materials Project
BaCaFe4O8 crystallizes in the trigonal P-31m space group. The structure is three-dimensional. Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share edges with six equivalent BaO12 cuboctahedra, edges with twelve equivalent FeO4 tetrahedra, and faces with two equivalent CaO6 octahedra. There are six shorter (3.00 Å) and six longer (3.19 Å) Ba–O bond lengths. Ca2+ is bonded to six equivalent O2- atoms to form CaO6 octahedra that share corners with twelve equivalent FeO4 tetrahedra and faces with two equivalent BaO12 cuboctahedra. All Ca–O bond lengths are 2.38 Å. Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three equivalent CaO6 octahedra, corners with four equivalent FeO4 tetrahedra, and edges with three equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 57°. There is one shorter (1.88 Å) and three longer (1.91 Å) Fe–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to one Ba2+, one Ca2+, and two equivalent Fe3+ atoms. In the second O2- site, O2- is bonded in a linear geometry to three equivalent Ba2+ and two equivalent Fe3+ atoms.